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Ginkgo Copies and Axolotl Crosses at the Museum

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Ginkgo Copies and Axolotl Crosses at the Museum

Compare trees grown from cuttings with offspring from two parents.

Part 1: The ginkgo courtyard

Read the passage and Table 1, then answer the questions.

Living Things in the Fossil Hall

1The fossil hall at the Lakeshore Museum of Natural History ends at a glass wall that looks out on a courtyard of ginkgo trees. The museum, the people and the numbers here are made up, but they are based on real plants and animals. A fossil leaf beside the window looks almost exactly like the fan-shaped leaves outside. Fossil leaves like it are found in rocks more than 100 million years old. Sixth grader Javier Lund spent a week with the museum's curator of living collections, Dr. Bettina Oduya.

2Each ginkgo tree is either male or female. In fall, female trees drop seeds with a soft, very smelly coat, so many cities plant only male trees. Fifteen years ago, the museum planted 24 ginkgos in the courtyard, all in the same soil and sun. Twelve were grown from cuttings, small branches cut from one male tree that rooted in moist soil. The other twelve grew from seeds of a female tree in the city park. Wind had carried pollen to her from male trees nearby. Every fall, Dr. Oduya records the day each tree's leaves turn fully yellow. The seedling trees turned out to be a mix of males and females.

3Next to the fossils of early amphibians, the museum keeps a tank of living axolotls, salamanders from lakes near Mexico City. Most wild axolotls are dark. The museum also raises white axolotls with dark eyes. Skin color depends on one gene. The allele for dark skin (D) is dominant, and the allele for white skin (d) is recessive. Each pair's young hatch from eggs the female lays after the pair mates.

Table 1. The Courtyard Ginkgos After 15 Years
Trees grown from	Trees	Day leaves turned yellow	Height (m)	Male trees
Cuttings of one tree	12	Oct 28 to Oct 30	8.0 to 8.6	12
Seeds of one tree	12	Oct 18 to Nov 9	6.1 to 9.5	5

1.

Use Table 1. Find each span by subtracting the dates: for example, Oct 5 to Oct 9 is a span of 4 days.

The trees from cuttings turned yellow over a span of days. The trees from seeds turned yellow over a span of days.

2.

All 12 trees grown from cuttings are male. Which explanation fits the passage best?

A. The courtyard soil and sun made each young tree grow into a male tree.B. Cuttings from a female tree rot before they root, so the gardeners lost those cuttings.C. Pollen from the park's male trees reached the cuttings and made them male.D. They grew from pieces of one male tree, so they carry that tree's genes.

3.

The trees grown from seeds varied much more in height and in the day their leaves turned yellow. Which explanation fits the passage best?

A. Each seed formed from pollen and an egg, so each seedling got a new mix of alleles.B. Each seed got its genes from the female tree alone, but the seeds dried out unevenly.C. The seedlings were younger, so they had not yet grown into copies of their mother.D. The seedlings were planted in different soil, so each one grew in its own way.

4.

Why does it matter that all 24 trees grew in the same courtyard soil and sun?

A. The male trees then make seeds that drop into the courtyard each fall.B. The trees then share pollen, so the cuttings slowly turn into seedlings.C. Differences between the two groups then come mostly from their genes.D. The trees in both groups then grow to the same height after 15 years.

5.

A city wants a row of ginkgos along a street that look alike, turn yellow together and never drop smelly seeds. Based on the passage and Table 1, which method fits these goals best?

A. Plant seeds from a female tree, since her seedlings grow more evenly in heightB. Root cuttings from one male tree, since the copies share its traitsC. Plant seeds from a male tree, since his seeds grow into male treesD. Root cuttings from a female tree, since her copies turn yellow early

6.

Sort each statement by the kind of reproduction it describes.

Part 2: The axolotl tank

Use paragraph 3 and Table 2. D = dark allele (dominant), d = white allele (recessive).

Table 2. Young From Three Axolotl Pairs
Pair	Mother	Father	Dark young	White young
1	Dark	Dark	186	62
2	White	Dark	101	99
3	White	White	0	150

7.

Both parents in Pair 1 are Dd. This Punnett square shows their cross. One box is missing.

Punnett Square: Pair 1
Mother ↓ / Father →	D	d
D	DD	Dd
d	Dd	?

The missing box is . For each young of Pair 1, the chance of white skin is %.

8.

What percent of Pair 1's young in Table 2 were white? %

9.

Look at the three dark boxes in the Pair 1 Punnett square and how many of them are Dd.

Of Pair 1's 186 dark young, about how many would you expect to be Dd, carrying a hidden white allele? young

10.

In Pair 2, the mother is white (dd). Which genotype does the dark father most likely have?

A. dd, because about half of the young came out white like the motherB. Dd, because about half of the young were white, so he passed on dC. DD, because a dark father passes a D allele to each of his youngD. DD, because more of the young were dark than white

11.

Dr. Oduya wants to know whether one dark young axolotl from Pair 1 is DD or Dd. When it grows up, which cross would tell her best?

A. Cross it with a white axolotl; any white young would show that it is Dd.B. Cross it with a dark sibling; dark young would show that it is Dd.C. Cross it with a DD axolotl; white young would show that it is Dd.D. Raise it alone in a tank; a change to white skin would show that it is Dd.

12.

Javier says, "Cuttings and two-parent offspring are the same thing. Either way, the young are copies of a parent." Do you agree? Write a claim, give evidence from both tables, and explain your reasoning. Compare asexual and sexual reproduction in your answer.